The deepening crisis has caused frayed relations on both sides. North Korea’s continued belligerence was a blow to China, which has failed to keep its ally in check despite persistent warnings. China said Monday it had made a “stern representation” to North Korea over the test.

Meanwhile Donald Trump, the US president, opened up a rift with South Korea, saying it risked “appeasement” of Pyongyang.

The developments represented a significant ratcheting-up of tension in the region, already on edge over North Korea’s rapidly intensifying missile-testing program.

Latest developments:

— Briefing parliament, South Korean military officials said there were ongoing signs that Pyongyang was preparing to test another Intercontinental ballistic missile (ICBM).

— Seoul said it would deploy four Terminal High Altitude Area Defense (THAAD) launch pads in response to the accelerating threats from the North.

— South Korea conducted a series of military drills, including a simulation of an attack on the North’s nuclear-testing site. More live-fire tests would follow, it said.

— The United Nations Security Council was due to hold an emergency session in New York.. Leaders of Japan and South Korea held a 20-minute phone call Monday to discuss tougher sanctions.

— The moves came after Pyongyang claimed it has the ability to place a miniaturized nuclear weapon on an ICBM, making it a direct threat to the United States.

South Korea’s response

Seoul responded to North Korea’s nuclear test with a show of military might that was intended to demonstrate its willingness to “wipe out” the regime of Kim Jong Un, South Korea’s Defense Ministry said.

South Korea’s army and air force carried out a joint drill that involved multiple F-15K fighter jets and surface-to-surface ballistic missiles. They hit targets off the country’s east coast to simulate a strike on North Korea’s nuclear test site, according to a statement from the South Korean Joint Chiefs of Staff.

At a Defense Ministry press conference, Major General Jang Kyung Soo, said South Korea had detected “continuous signs” that North Korea was preparing another ICBM test. He said the North could launch the missiles ahead of September 9, the anniversary of the day North Korea was founded, in a show of celebration at home and defiance to the US.

He said South Korea plans to carry out another missile drill to show its “strong will and ability to respond.”

Rift with Washington

President Trump has not thought to have spoken with his South Korean counterpart, President Moon Jae-in, since Sunday’s hydrogen bomb test, though US and South Korean military advisers have been in touch. Instead, Trump warned South Korea in a Twitter message Sunday that “talk of appeasement” would not work.

It was unclear what prompted the comment. In the past, President Moon has advocated dialogue with Pyongyang. Moon’s office responded by reiterating the government would “pursue the denuclearization of the Korean Peninsula through peace with our allies.”

Adam Schiff, the top Democrat on the US House of Representatives Intelligence Committee, cautioned against criticizing South Korea.

“I’m sure that Pyongyang enjoys seeing us fight with our own ally in the region,” Schiff said. “We need to be working hand in hand with South Korea and with Japan… why we would want to show divisions with South Korea makes no sense at all.”

China embarrassed

Pyongyang’s actions appear, in part, designed to test the limits of China’s support. Experts say its latest nuclear test could have been timed to coincide an international economic summit currently being hosted in Beijing.

North Korea has timed missile tests this year to coincide with other important Chinese events, including a missile test during a summit in May on China’s “Belt and Road” regional economic initiative.

Geng Shuang, a spokesperson for the Chinese Foreign Ministry said Bejing had “launched stern representation” to North Korea over its nuclear test. In a regular press briefing Monday, Geng said the test was “wrong” and “against the will of the international community and will meet with China’s disapproval.”

He said China opposed North Korea’s missile development program and said it wanted to return to six-party talks as soon as possible.

Responding to a question about the deployment of more US military assets in the region, Geng said China hoped all sides would “work to ease the tension instead of escalating the tension.”

Trump criticized China in his series of tweets Sunday, saying North Korea’s actions were a “great threat and embarrassment to China, which is trying to help but with little success.”

Trump also said that the US was considering cutting off all trade with any country that carried out business with North Korea. That would include China, which provides an economic lifeline to North Korea. China is the largest US trading partner in terms of goods, and a trade war between the two nations could be devastating.

International response

The UN Security Council was due to meet in emergency session Monday, the second in a week.

US and its allies are looking to push through a new package of sanctions, including measures to restrict oil shipments to North Korea, US officials said. Most of North Korea’s oil comes from China, and the US believes that stopping these shipments would place severe pressure on the North Korean regime.

After meeting last week in response to North Korea’s launch of a missile that flew over the northern Japanese island of Hokkaido, the UN stopped short of announcing additional restrictions on top of those already passed in early August. Those are some of the most stringent to date, and the Trump administration has started punishing companies for doing business with North Korea — so-called “secondary sanctions.”